1. Field of the Invention
This invention relates to a guidance seeker system for projected munitions. More particularly, the munition includes a plurality of photoconductive sensing elements that both enable calculation of a variance between the flight axis of the munition and an illuminated target and trigger at least one on-board diverter to reduce that variance.
2. Description of Related Art
Projected munitions frequently include a guidance seeker system that enables the projectile to calculate a variance from a target and to make one or more in-flight course corrections to increase the likelihood of the projectile disabling or destroying the target. One such guidance seeker system is disclosed in U.S. Pat. No. 5,529,262 by Horwath that discloses a guidance seeker system actuated via a continuous beam of ultraviolet, visible or infrared light. This seeker system includes a reticle with concentric, alternating, bands of light transmitting and light non-transmitting rings. The beam generates pulses as the target moves across the reticle field. The periodisity of these pulses is used to determine deviation of the target from a center line of the reticle. Circumferential thrusters on the projectile are then used to effect a necessary course change.
U.S. Pat. No. 6,076,765 by Horwath utilizes a reticle having a pattern discontinuity effective to generate a singly periodic pulse once each projectile revolution. The periodisity of pulses generated by the target sweeping across the reticle field enables the projectile to determine the line of flight variance between the projectile and the target. The singly periodic pulse enables the projectile to determine its rotation position. Utilizing this information, an appropriate ring diverter is fired to reduce or eliminate the variance.
Both U.S. Pat. Nos. 5,529,262 and 6,076,765 are incorporated by reference in their entirety herein.
Spinning reticle-based guidance seeker systems require a constant light source. Throughout this patent application, light is not limited to the visible spectrum, but includes infrared, ultra-violet as well as other portions of the spectrum. Typically, an infrared source on the target is utilized, i.e. a xe2x80x9cheat seekingxe2x80x9d missile. Such systems where the seeker is drawn to a light source originating on the target are referred to as passive guidance systems.
A semi-active guidance system guides a projectile to a target that is externally illuminated. Typically, external illumination is by a laser beam. The laser generating this laser beam may be mounted on the projectile, or alternatively, located on a separate platform, such as a helicopter or spotter plane. One semi-active guidance seeker system is disclosed in U.S. Pat. No. 5,102,065 to Couderc et al. This patent discloses a homing system utilizing a laser that tracks both a target and a missile. The homing system determines the variance between the two and transmits course correction instructions to the missile that are then effected by small explosive charges or rudder adjustments.
U.S. Pat. No. 5,835,204 to Urbach, that is incorporated by reference in its entirety herein, discloses pulsed laser systems utilized to determine the distance to a target.
The above mentioned guidance seeker systems require a steady state target signal or a steady state illumination signal from a target designator. They may also be amenable to pulsed signals having a repetition rate much faster than the highest frequency signal generated by the seekers.
To reduce the power required, and therefore the size and cost of laser designators, it is desired for the laser designator to be a low repetition rate laser that generates pulse sequences too slow for the operation of the prior art guidance seekers. There remains, therefore, a need for a guidance seeker system effective for use with low repetition rate pulse lasers that may be utilized with either spinning projectiles or nonspinning projectiles.
Accordingly, it is an object of the invention to provide a guidance seeker system useful to guide missiles or other projected munitions to a target.
It is a feature of the invention that the guidance seeker system is useful with both pulsed and nonpulsed target designators and with both spinning and nonspinning projectiles. Another feature of the invention is that the guidance seeker system includes an optics package having a plurality of photoconductive sensing elements. These photo-conductive sensing elements are electrically coupled to one or more diverters that are disposed about an exterior surface of the projectile. Selective firing of diverters guides the projectile to the target. Another feature of the invention is that the optics package includes a lens system that transmits the target designator beam to the photoconductive sensing elements as either a focused spot or as a defocused spot.
It is an advantage of the invention that the guidance seeker system is useful with target designators that generate beams of short pulses with slow pulse repetition rates and may be used to discern coded laser pulses. Another advantage of the guidance seeker system of the invention is that it calculates and corrects for variance from a target utilizing a focused beam. When used in a defocused beam mode, the seeker system determines and corrects for both variance and projectile rotation. Still another advantage of the invention is that in certain embodiments, the guidance seeker system includes a recirculating shift register that compensates for a prefired or otherwise inactive diverter.
In accordance with the invention, there is provided a guidance seeker system effective to guide a projectile to a target comprising an optics package disposed at a forward end of the projectile. The optics package includes a plurality of photoconductive sensing elements and has a lens disposed between the target and the photoconductive sensing elements at a distance, D, from the photoconductive sensing elements. A plurality of course diverters are mounted on an exterior surface of the projectile wherein illumination of one or more of the photoconductive sensing elements causes the plurality of course diverters to reduce a variance between a present flight path of the projectile and the target.
The above stated objects, features and advantages will become more apparent from the specifications and drawings that follow.